(a). Field of the Invention
The invention relates to a method for an impurity distribution simulation for use in a semiconductor manufacturing process.
(b). Description of the Related Art
A conventional technique to simulate an impurity distribution in a semiconductor manufacturing process which includes a combination of an ion implantation and a thermal diffusion steps will be described first. FIG. 1 is a flowchart of the conventional technique used to simulate an ion implantation and a thermal diffusion steps.
Initially, at step T1, a decision is made whether or not a subject step to be simulated is an ion implantation. If it is an ion implantation, the ion implantation simulation is performed at step T2.
There are two categories in methods for simulation which have been used for an ion implantation, including an analytical method and a Monte Carlo method. An ion implantation simulation for an arbitrary multilayer structure using an analytical technique can be made by expanding a method for a two-layer structure which is described in an article entitled "Models for Implantation into Multilayer Targets" by H. Ryssel, J. Lorens and K. Hoffmann in Appl. Phys. A41, 201-207(1986).
If it is determined at step T1 that this is not an ion implantation step, it is determined at step T3 whether or not the step to be performed is a thermal diffusion. If a thermal diffusion is to be performed in this-step, a thermal diffusion simulation takes place at step T4. After performing an ion implantation simulation or a thermal diffusion simulation after step T2 or step T4 in FIG. 1, it is determined at step T5 whether all the steps have been completed. If not, the operation returns to step T1, repeating the above described procedure.
A simulation technique for the thermal diffusion known in the art are conducted in two ways, one not considering and another considering a point defect distribution. In order to effect a simulation with a good accuracy for a semiconductor manufacturing process, which includes an ion implantation and a thermal diffusion steps, it is essential to use a thermal diffusion simulation which tales a point defect distribution into consideration. To effect a thermal diffusion simulation which consider the point defect distribution during the thermal diffusion step, it is necessary that a point defect distribution which occurs during the ion implantation be continually calculated. At this end, a simulation for the ion implantation step should be conducted in the conventional technique by using Monte Carlo method in the ion implantation simulation.
However, there is a problem in conducting the Monte Carlo method in the ion implantation simulation in that it requires an increased length of time for the calculation. This is because the Monte Carlo method performs a simulation of a scattering process for each ion implanted in a statistical method, in which the calculation for one ion implantation simulation should cover at least 1,000 to 10,000 ion particles. In practice, when such a simulation is conducted for phosphorus ions at an energy on the order of 1,000 keV and for a number of particles, which is 10,000 for example, the calculation requires 10 hours or longer using a work station of, for example, model 95MIPS, 54SPECfp92.